Highly concentrated supersonic liquified material flame spray apparatus has been developed within recent years utilizing an internal burner as the source of the jetlike flame. Such internal burner type devices for the flame spraying of powdered material are in common commercial use, as evidenced by detonation gun type apparatus as well as the ultra-high velocity flame spray apparatus evidenced by my U.S. Pat. No. 4,416,421. In that patent, in particular, powdered material or a solid wire is are fed into the nozzle inlet of a venturi type nozzle remote from the combustion chamber of the internal burner itself or at a point just ahead of the throat of the nozzle bore to insure a concentrated and highly focussed core of spray material passing down a relatively long nozzle flow path downstream of the throat exit from the nozzle and material spray coating on a substrate downstream of the nozzle exit end. When using a material source taking the form of wire rods, in practice, difficulties arise in the feeding of the wire. In a system, for instance, evidenced by FIG. 4 of U.S. Pat. No. 4,416,421, the wire is heated, atomized and the liquid spray droplets as a result of atomization are carried at the core of the gas stream for deposition on the substrate downstream from the exit end of the nozzle. Under optimum operating conditions, excellent coatings at high deposition rates are produced. One of the major difficulties encountered includes the straightness of the wire being fed. As an example, a commonly used nozzle such as nozzle 42 of FIG. 4 has a diameter of only five-sixteenths of an inch and a length of six inches. In practice, it is difficult to find a wire straightener capable of straightening coiled wire sufficiently to permit its use with a nozzle having these dimensions. In addition, the disadvantage exists that it is possible to plug the nozzle when the wire motion stops, preventing further feed of the wire.
It is therefore a primary object of the present invention to provide a method for introducing wire rod material into a supersonic flame jet, particularly useful in internal burner type of flame spraying apparatus in which the wire rod being fed may curl or have a tendency to curl without interfering with the feeding of the wire, and wherein it is virtually impossible to plug the nozzle when wire motion stops.